A poll shows 40% of Catholics support independence, compared to just 17% of Church of Scotland members.
Parliamentary officer for the Catholic Bishops' Conference of Scotland, John Deighan, told Premier it could be down to a shift in attitudes north of the border.
He said some Catholics previously felt discriminated against in Scotland because of their faith.
He added: 'I worked in an engineering environment before and I had people say, "Don't let the guy in the warehouse know you're a Catholic or he won't give you the equipment you need."
'Things like that happened, I think that's not so much the case now.
'The opposition then was between Catholic and Protestant, that has changed radically.'
A study carried out by Stirling University found that Catholics and people of no faith were the most likely to vote yes.
John Deighan told Premier that the SNP, which is campaigning for yes, has done a lot of work to appeal to Catholic voters.
'The party has been marked by a determined effort to put Catholics at ease with the SNP.
'They've spoken out very strongly in favour of Catholic schools, they've had a good social relationship with Cardinal O'Brien in particular, Cardinal Winning before him.
'So they're not being seen as a threat to the Catholic community as they once would have been,' he said.
Scots will be asked the yes/no question: 'Should Scotland be an independent country?' on September 18.
The Yes campaign is also claiming that independence would help fight poverty.
Currently, one in five Scottish children are living in poverty and John Deighan said taking a strong line on this will appeal to Catholics.
'Catholics would feel quite comfortable with the rhetoric of social justice or the important emphasis on it.
'Dealing with the poor and supporting communities.'
The 2011 census revealed that 15.9% of people in Scotland identified themselves as Roman Catholic.